It is known to thicken vinyl ester resin compositions by the admixture of (1) a metal oxide or hydroxide, such as magnesium or calcium oxide or hydroxide, and (2) water to the vinyl ester resins containing reactive carboxyl acid groups. See, for example, U.S. Pat. Nos. 3,466,259 and 3,548,030. As noted in these two patents, among others, it is necessary to first prepare vinyl esters by reacting an ethylenically unsaturated monocarboxylic acid with a polyepoxide and then post-reacting the resulting ester with a cyclic dicarboxylic acid anhydride. The resulting modified vinyl ester is then thickened by the admixture of Group II metal oxides or hydroxides and water.
A simplified method for preparing thickenable vinyl ester resin compositions has now been found which does not require a two-step process for the vinyl ester compositions, does not require the use of a dicarboxylic acid anhydride and does not require the presence of water.